In a radio communication system, the use of the MIMO (Multiple-Input Multiple-Output) technology and the beamforming technology makes channel information indispensable. A beamformer obtains channel information using the feedback from a beamformee, and uses the channel information as a reference for subsequent data transmission.
In the conventional art, the process of obtaining the channel information by the beamformer is as follows: The beamformer transmits an NDPA (Null Data Packet Announcement) and an NDP (Null Data Packet) to a beamformee to request the channel information; after receiving the NDPA and the NDP, the beamformee estimates the channel between the beamformer and the beamformee, and transmits the channel information to the beamformer according to a rule. When the beamformer obtains multi-user channel information, for beamformees other than the first one, a Sounding Poll frame may be transmitted to instruct the other beamformees to feed back their channel information.
The beamformer, before transmitting data each time, obtains a TXOP (Transmission opportunity) in a contention mode, and then transmits data within the duration corresponding to the TXOP. When the beamformer requests the channel information within the duration of a TXOP, if the channel information obtained by the beamformee fails to be completely transmitted before the duration of the TXOP ends, the beamformee may feed back a null feedback frame to notify the beamformer that the channel information cannot be fed back currently and the cause thereof, and meanwhile, the beamformee discards the estimated channel information. If the beamformer still needs the channel information, the beamformer can only retransmit a channel estimation request after obtaining a TXOP again, and the beamformee performs channel estimation again and then transmits the channel information to the beamformer.
During the implementation of the present invention, the inventor finds that the prior art has at least the following disadvantages:
The beamformer repeatedly transmits the NDPA and the NDP to request the channel information, causing a low efficiency and a waste of the resources. In addition, the beamformee repeatedly performs the channel estimation, causing a power waste.